Navicular Syndrome

Navicular syndrome is a debilitating condition for the horse that, in reality, does not exist. Like colic, it is a generalised reference, in this case to pathologies of the leg – principally the foreleg. Although we might find many references to navicular syndrome in popular equine literature, there is no scientific reference that specifies and pinpoints the problem. Nevertheless, we do find frequent reference, even in the scientific world, to the treatment of navicular syndrome. This makes the whole subject even more mystifying since we now have all sorts of scientifically based treatments for a condition that the scientific world considers does not exist!

So, what is going on? Well clearly there is a problem and, as with many things equine, “military solutions” were cooked up to appease the Sergeant-Major and allow him to log the reasons why a horse could not perform: digestive problems not further explainable – colic; locomotion problems not further explainable – navicular syndrome. Why navicular? Probably because often the problems could be localised in the lower part of the leg and, anatomical analysis had revealed, the navicular bone was a small and rather unusually placed bit of kit. It was clear enough that it acts as a necessary pulley for the deep digital flexor tendon (DDFT) to do its work connecting the deep digital flexor muscle (DDFM) with the coffin bone or third phalanx (P3) but the interaction of all the various parts was clearly not well understood – and this is still often the case.

Even today, veterinary “specialists” will take X-ray photographs of the navicular bone and blame any number of things they might see on its “dysfunction”. They will then attempt a succession of procedures in order to alleviate the pain and make the problem go away. They may apply special shoes which will often work…for a short while; when this begins to lose effect after a few weeks, they might then attempt to apply reversed shoes “to give more support at the rear of the hoof…” but, once again, the effect starts to wear off. The next stage might be to apply shims between the shoes and the hoof – with the idea of raising up the hoof to “lower tension on the DDFT” but, as before, this is just another short term workaround of the problem. Then they play the trump card – cut the nerves to this part of the leg; that way, the horse will no longer be in pain.

Very true; the signal that something is wrong no longer gets through to the horse. We can liken this to the oil warning light in the car. As a driver, we see the light go on and so we take the car to the garage. The garage mechanic tinkers around (maybe he washes the windscreen, changes the tyres, fills up with petrol… ) but the light still doesn’t go out. So, the easiest thing now is simply disconnect the light – and we won’t see the problem any more… And this is what many so-called reputable veterinary surgeons do – and the horse continues working, making the problem worse.

In a video from March 2016 (TheHorse.com) of a talk by Dr Jim Schumacher of the University of Tennessee’s College of Veterinary Medicine, it is reported that all the (traditional) methods of treatment combined will not extend the horse’s relief from symptoms for more than 18 months. At that point, there is nothing more that can be done for the horse and it will probably have to be retired or maybe even put down.

Lowering tension on the DDFT

This is one the big fallacies we face in the story; supposedly it is too much tension in the deep digital flexor tendon that can give rise to navicular syndrome. For this reason, we raise the heel to “lower” the tension. But, tendons are intended to be under tension. That is their function. It is also their saviour. If a tendon is not maintained at full extension, any shock action – a rapid jerk, for instance – is likely to cause some damage. The tendon is an incredibly tough structure and is rarely likely to suffer damage itself under such circumstances; rather it is the point where tendon and muscle, or possibly tendon and bone, are fused together. This is like in any chain, a weak point. Damage to the tendon itself is more likely to be the result of a direct trauma – a shod rear hoof hitting the back of the tendon extremely hard or repetitively.

If the DDFT tension is lowered, the horse will try to compensate. The deep digital flexor muscle will tense up to “take up the slack” in the DDFT but this almost permanent tensing of the DDFM brings with it yet more pathologies. Muscles are not designed to be permanently under tension – that is their “working” conformation and all muscles are intended to rest, even if it is only for a few (milli)seconds at a time. The heart is a good example: it beats on average slightly more than once a second throughout our whole life; each beat is a series of muscular contractions and relaxations; but the muscles of the heart relax for several milliseconds, with every beat; only with every stimulus to beat, do the muscles actually contract. Back problems are the most predominant in horses where the caudal structures of (particularly) the front hooves are too high.

The real problem

An incorrect conformation will have manifold effects upon the body. Of this, most experts are in agreement but the way forwards is so often muddied by misconceptions, inaccurate analysis, misplaced diagnosis – and subsequent treatment – and a wholly unscientific lack of logic. And when the treatment of one pathology results in another, confusion reigns. The reason for this is often simple; the tendency in the medical world, both human and veterinary, is to treat symptoms rather than causes. But if we only treat the symptoms, the cause is still there and will, in time, either create the same symptoms all over again or displace the symptoms to a new location. Essentially the latter is what we repeatedly see in cases of navicular syndrome. The actual cause is left unaddressed and the symptoms are simply shuffled around the leg a bit.

What happens with navicular syndrome has quite a rational explanation which makes it nothing more than astounding that the medical world continues to act in the way it does. That the farriers continue unabated is less surprising but maybe the reliance of the vets on the farrier for all matters leg and foot explains the resistance to education by the vets, and indeed ultimately the farriers.

In any structure, biological or manmade, where one surface rubs over another, a protective layer is incorporated to reduce wear and tear. This layer needs replacing regularly otherwise it will wear to the point of being ineffectual. In vehicles, we see this in tyres, the rubber or metal tyre wears down but protects the rim carrying it; when the tyre is thin, we replace it with a new one. Brake linings are the same; the brake pads wear as they rub on the disc (which also wears but at a much lower rate) and before the lining is completely worn away, we must replace it – otherwise the metal backplate of the pad starts to rub on the disc damaging both the backplate and the disc.

The tendons are the same. They are enclosed in a protective sheath and at the point that they pass over another surface – knees, elbows, ankles etc. – they are protected even further by the synovial bursa. This synovial bursa is like our brake linings or tyres and prevents abnormal wear of the tendon or the surface it is passing over. The synovial bursa creates an enhanced rubbing surface that is more resistant to wear than either the bone or the tendinous sheath. Furthermore, this sheath is designed for such wear and as such is continually renewing itself.

The extent of the synovial bursa is different from animal to animal – even from leg to leg. But every animal is built more or less millimetre perfect. When farriers apply shoes to a horse’s hoof (or possibly even when the hoof is simply allowed to grow too long in the caudal structures), the millimetric alignment of the internal structures is disturbed; in the case of navicular syndrome, the protective bursa is no longer protecting either the navicular bone nor the tendon that is rubbing against it. The farrier’s trick of applying special shoes, shifts the point of contact a few micrometres up the tendon away from the painful spot, alleviating the pain. But there is still no protective bursa which means that, after a short while – experience and study shows it often to be less than two weeks – the pain starts to return. After a month, the farrier will have to jiggle the shoes around again in order to alleviate the pain at the new point… And this goes on until it becomes clear that the problem is not going to be solved by jiggling shoes and shims around.

The Solution

The solution should now be evident. Realign the navicular bone with the protective bursa. This is achieved relatively very simply – a progressive lowering of the heels and a reeducation of the horse over a period of a few months. Reeducation is a necessity because in the majority of cases, the horse has been shod for a long period of time and will have all the pathologies associated with shoeing. This means it will not necessarily be easy to treat but a great deal of that lies with the dedication of the owner, not with the treatment and certainly not with the horse.